Graining printing plates



Jan. 8,- 1963 M. w. wRucK GRAINING PRINTING PLATES 2 Sheets-Sheetl Filed March 2. 1959 INVENTOR. W Wrack BY dfb.

Jan. 8, 1963 M. w. wRucK 3,072,

GRAINING PRINTING PLATES Filed March 2. 1959 2 Sheets-Sheet 2 zs IL E' 5 n &

n I Q) Q n '3 I .S fill II I 2% I Q [b I [L T x INVENTOR. Max M Wrunk Patented Jan. 8, 1963 3,072,546 GRAINING PRINTING PLATES Max Waldemar Wruck, Spokane, Wash., assignor of onehalf to Lawton Printing Company, Spokane, Wash., a corporation of Washington Filed Mar. 2, 1959, Ser. No. 796,346 3 Claims. (Cl. 204-141) My invention relates to the graining of printing plates. 'It is the purpose of my invention to provide an aluminum printing plate with a grained surface of water insoluble aluminum compounds which is uniformly fine and which is made up of a surface layer in which there are crevices that extend down to the solid metal of the plate. The surface layer is composed of particles of Water insoluble aluminum compounds adhered to the surface and to each other to form the roughened or grained surface.

It is also a purpose of my invention to provide a method of graining printing plates of aluminum which is of such nature that I can obtain uniform fine graining of the plates in any size desired, the method being one of immersing the plates in a dilute hydrochloric acid solution at an controlled temperature and subjecting the immersed plates to an alternating current discharge between plates at a temperature of 15-26 degrees C. for 25 to 35 minutes, then washing the plates and boiling them in water to which oxalic acid is preferably added and finally cleaning the plates to remove any loose particles. The plates so prepared have a uniformly fine surface coating of aluminum hydroxide particles. The coating upon examination appears to have crevices between particles which enable the surface to retain inks, etc., readily.

The nature and advantages of my invention will appear more fully from the following detailed description and the accompanying drawings which illustrate the preferred method and means of carrying out the invention.

In the drawings:

FIGURE 1 is a somewhat diagrammatic plan view of the treating tanks used in my invention;

FIGURE 2 is a sectional view taken on the line 2-2 of FIGURE 1; and

FIGURE 3 is a sectional view taken on the line 3-3 of FIGURE 1.

In carrying out my invention I preferably use sheets such as shown at 5 of substantially pure aluminum. The

sheets to be satisfactory for my purpose, must be uni-' formly smooth on the surface with no apparent scratches or blemishes. These sheets are cleaned to remove any grease or dirt thereon. The cleaned sheets are then clamped between clamp bars 6, 7 and 8 to support them in the proper relation to each other during the graining steps. As shown, the several clamp bars 6 are non conductors, but they have conducting strips 9 set into one side face thereof to engage one of the sheets 5. The clamp bar 7 is also a non conductor, but it has a strip 10 set into one side thereof. The clamp bar 8 doesnt need any conductor. The several clamp bars 7 are placed between the clamp bars 6 and 8, as shown in FIGURE 1. This enables me to place one sheet 5 between each bar '6 and the adjacent bar 7 and two sheets 5 back to back between each pair of bars 7. Suitable clamps 11 and 12 are used to clamp the several bars 6 and 7 together, and serve also to lift the assembled clamp bars and sheets from one place to another.

The alternate pairs of sheets 5 will be engaged by conducting strips 9 which engage one bus bar 14 and the conducting strips 9 which engage another bus bar 15. The single sheets 5 at the outside of the group next to the bar 8 is engaged by a strip 9. The strip 10 engages the other single sheet 5. The bus bars 14 and 15 are connected to a source of alternating current through a suitable transformer 16 to provide the proper voltage between the/sheets 5. This arrangement enables me to grain the outer surfaces of two sheets 5 between each pair of clamp bars 6.

The sheets 5 are first placed in a weak hydrochloric acid in water solution in the tank 1 This solution is of about /2 Baum to 1 Baum strength. It is important that the temperature be within a narrow range, preferably about 15 degrees C., although higher temperatures up to 26 degrees C. may be used. If the temperatures are higher, then the time the sheets are treated in the bath must be increased in proportion. I keep the sheets in the bath for a period of 30 minutes when the temperature of. the bath is between 16 and 20 degrees C.

The sheets 5 while in the bath, are subjected to alternating current. They are spaced apart by the clamp bars 6 to hang an inch from each other surface to surface. An alternating current of 50 to 60 cycles is entirely satisfactory. The spacing of the sheets must be carefully controlled. They may be spaced apart as little as inch and as much as 1 /8 inch, but the best spacing, I have found, is approximately 1 inch. The voltage between sheets should be less than 11 volts but more than 5 volts. Excessively high voltage makes the sheet surfaces very rough. Too low voltage will notmake enough deposit on the sheet surface. I find the best voltage to be 8 volts.

The reaction of the sheets to the solution during treatment generates heat so it is necessary to cool the tank 1 by circulating cooling water around it. The tank is made of non-conducting material for electricity, of course.

By the foregoing arrangement the sheets are alternately positive, then negative with respect to the sheets spaced from them. This results in removal of aluminum from the surface of each plate and deposits of fine hard particles on the surface of each plate. The particles adhere firmly to the surface making a very fine graining with crevices between the accumulated grains. Care must be taken to limit the time in which the electrolytic action is permitted to take place. If it is stopped too soon there is not enough deposit on the surface and if it is continued too long, the deposit becomes uneven and coarse. Repeated tests have shown that optimum results are obtained when the time of treatment is about 28 to 32 minutes and the temperature of the solution is about 15 to 20 degrees C. If the temperature is kept higher, the time required is longer. If the temperature is kept lower, then the time must be shorter. A maximum temperature up to 26 degreesC. can be used it slows the process too much.

The plates, after the electrolytic action, are placed in a tank 2 and washed well with plain water at about 12 to 15 degrees C. to remove all traces of the acid. The plates are then immersed in a tank 3 in boiling water and held in the boiling water for 5 to 15 minutes. The boiling time is not critical but the sheets must be subjected to temperatures of about degrees C. A weak solution of oxalic acid is beneficial in that it makes the surface deposit lighter in color.

The boiling in oxalic acid solution is followed by scrubbing the plate thoroughly with plain water to remove any loose material and final drying. The surface layer or grain remaining on the sheet is insoluble in water and provides an exceptionally fine hard grain to receive the printing fluids. Since the treatment is entirely in baths, the plates can be made of any desired size within the dimensions of the tanks and the clamp bars.

The initial action is electrolytic wherein the action of the hydrochloric acid with the electric current produces a Water insoluble coating of fine particles on each sheet which are finally fixed by the boiling in water or in the oxalic acid solution to produce a fine grained surface. The surfaces to be grained must be opposite each other and uniformly spaced apart. Graining does not take place on the outside surfaces of the end plates where there is no like surface opposite to them.

The sheets produced by my method have the formerly smooth surface roughened by the removal of some aluminum. They have this rough surface obscured by a covering of hard aluminum hydroxide particles which are quite uniformly laid on the surface. In the case of boiling'in the oxalic acid solution the particles are in part converted to aluminum oxalate, which is a hard, water insoluble product.

My improved lithographic printing plate has a much finer and more uniformly grained surface when compared with conventional tub-grained aluminum and zinc printing plates. When used, the plates have been found to make excellent reproductions especially in reproduction of half tones. The plates are remarkably free of oxidation. They have been removed from a press without gumming and allowed to stand for as long as ten days and have subsequently been put back on the press, washed with Water and have successfully continued printing runs with no visible trace of oxidation.

It is believed that the nature and advantages of my invention will be clear from the foregoing description.

Having described my invention, I claim:

1. In the making of grained aluminum printing plates, a method of producing the grained surface Which comprises subjecting opposed surfaces of two plates to an alternating current of about 8 volts while they are immersed in a hydrochloric acid solution of /2 Baum to 1 Baum strength in Water at a spacing of to 1 /2 inch and at a temperature of about 15 degrees C. to 26 degrees C. for a period of 25 to 35 minutes, then removing the acid from the plates and boiling them in water.

2. In the making of grained aluminum printing plates, a method of producing the grained surface which comprises subjecting the faces of the plates to be grained to an alternating current of more than 5 but less than 11 volts while they are immersed in a hydrochloric solution of /2 Baum to 1 Baum strength of acid and spaced 4 to 1%; inch from a like aluminum surface and while they are maintained at a temperature between 15 degrees C. and 26 degrees C. for a period of to minutes, removing the acid solution and immersing the plates in boiling water.

3. In the making of grained aluminum printing plates, a method of producing the grained surface which comprises subjecting the faces of the plates to be grained to an alternating current of more than 5 but less than 11 volts while they are immersed in a solution of /2 Baum to 1 Baurn strength of hydrochloric acid and spaced to 1 /8 inch from a like aluminum surface and while they are maintained at a temperature between 15 degrees C. and 26 degrees C. for a period of 25 to 35 minutes, removing the acid solution and immersing the plates in boiling water.

References Cited in the file of this patent UNITED STATES PATENTS 737,882 Strecker Sept. 1, 1903 1,256,954 Travers Feb. 19, 1918 1,644,597 Lichtenstein Oct. 4, 1927 1,853,437 Kuttner Apr. 12, 1932 1,946,147 Bengsten Feb. 6, 1934 2,107,318 Work Feb. 8, 1938 2,119,031 Wescott May 31, 1938 2,209,712 Brennan July 30, 1940 2,336,846 Clark Dec. 14, 1943 2,344,510 Hagelin Mar. 21, 1944 2,598,043 Eichner May 27, 1952 2,681,310 Wood June 15, 1954 2,685,563 Gauthier Aug. 3, 1954 2,699,382 Altenpohl Jan. 11, 1955 2,888,387 Wasserman May 26, 1959 

1. IN THE MAKING OF GRAINED ALUMINUM PRINTING PLATES, A METHOD OF PRODUCING THE GRAINED SURFACE WHICH COMPRISES SUBJECTING OPPOSED SURFACES OF TWO PLATES TO AN ALTERNATING CURRENT OF ABOUT 8 VOLTS WHILE THEY ARE IMMERSED IN A HYDROCHLORIC ACID SOLUTION OF 1/2 BAUME TO 1 BAUME STRENGTH IN WATER AT A SPACING OF 3/4 TO 1 1/2 INCH AND AT A TEMPERATURE OF ABOUT 15 DEGREES C. TO 26 DE- 